I received this notification from Telkom on one their 3 GB accounts, and the maths made me check again. But they did indeed cap me, as promised 
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Dear TelkomInternet subscriber,
Herewith a notification to inform you that your current usage reflects the following:
Username: [email protected]
Uploaded: 2.05GB
Downloaded: 2.74GB
Combined Total: 4.79GB
You have reached 80% of your monthly 3.00GB cap on both up- and downloaded traffic combined. Please note that you will be redirected to a throttled international service once you reached the cap limit. You have 259.89MB of bandwidth usage left before the constraint will apply.
To unsubscribe from this messaging service or view your online usage graphs, go to http://adsl.telkomsa.net
Thank you for choosing TelkomInternet, we value your dedicated support.
Regards,
TelkomInternet
--------------------------------
Dear TelkomInternet subscriber,
Herewith a notification to inform you that your current usage reflects the following:
Username: [email protected]
Uploaded: 2.05GB
Downloaded: 2.74GB
Combined Total: 4.79GB
You have reached 80% of your monthly 3.00GB cap on both up- and downloaded traffic combined. Please note that you will be redirected to a throttled international service once you reached the cap limit. You have 259.89MB of bandwidth usage left before the constraint will apply.
To unsubscribe from this messaging service or view your online usage graphs, go to http://adsl.telkomsa.net
Thank you for choosing TelkomInternet, we value your dedicated support.
Regards,
TelkomInternet